1. Field of the Invention
This invention relates to a modular backpanel interconnect system capable of providing optical and electrical interconnections between components housed within an integrated rack, as well as input/output connections and rack-to-rack interconnections. The invention is particular suited for, though not limited to, military avionics applications such as the proposed "optical backplane interconnect system" (OBIS).
2. Discussion of Related Art
The type of backplane with which the present invention is concerned typically extends along the back surface of an enclosure or integrated rack of the type used in avionics systems. The rack supports electronic components which plug into the backplane from the front and provides interconnections between the components as well as input/output connections to control systems in the airplane and rack-to-rack interconnections, and is designed to facilitate removal and replacement of components with a minimum of downtime, thereby significantly improving flight readiness.
Each of the components performs a control, sensing, or recording function and is typically in the form of a circuit card utilizing very high speed integrated circuitry (VHSIC) technology contained within a sealed metal housing to form a package known as a line replaceable module (LRM). Descriptions of line replaceable modules and integrated racks therefor are found U.S. Pat. Nos. 4,808,115 and 5,234,348.
While systems employing purely electrical line replaceable modules have been employed in military avionics for many years, current development has concentrated on the integration of optical interfaces into the modules. Optical interfaces provide higher bandwidth connections than is possible with purely electrical interconnections, and may be used in connection with such functions as multi-sensor integration, data fusion, image processing, and Automatic Target Recognition.
The present invention is part of that effort, but concerns the backplane into which the modules are plugged rather than the modules themselves, or the connectors which are provided on the modules. It was developed in connection with a program known as the optical backpanel interconnect system (OBIS), whose objective is to provide a compact and easily serviceable backpanel assembly for use in connection with line replaceable modules having different data rates and protocols, with data rate and communication restrictions imposed by the optical backplane being limited only by the capability of the passive optical interconnections, the switching functions being provided by one of the line replaceable modules, known as the fabric module, so that the backplane can be used to interconnect a variety of different functional elements simply by appropriately designing the fabric module.
Although the present invention is designed to meet the OBIS specifications, it is not limited thereto, and features of the invention will have applicability to component rack systems used in fields other than military avionics, such as the next generation of commercial aircraft, including systems other than those employing line replaceable modules. However, unlike prior purely optical fiber optic connector modules or patch panels of the type commonly used in other industries, such as the telecommunications industry, the OBIS-type systems with which the present invention is concerned must meet rigid space and reliability requirements, and must share the space with electrical power lines, which are necessary to provide power, ground, and low speed control lines, as well as to permit backward compatibility. As a result, prior optical interconnect systems offer few solutions to the problems addressed by the present invention, and are cited here primarily as background. Examples of such prior purely optical interconnect systems, primarily for use in telecommunications type optical connector modules, are found in U.S. Pat. Nos. 5,513,293, 5,412,497, 5,363,465, and 5,204,929. Also of interest as background are prior optical interconnect systems which also include electrical connectors, including the above-cited U.S. Pat. No. 4,808,115 which describes a line replaceable module connector including optical and electronic connections, but not a modular backplane, U.S. Pat. Nos. 5,037,313 and 5,611,013, which also describe opto-electronic connectors but not in connection with either a line replaceable module or a rack system, and U.S. Pat. No. 5,486,113, which is representative of a number of references describing purely electrical backplanes designed to provide purely electrical connections between components having different requirements. None of the connectors or interconnection systems described in these patents is suitable for use in the OBIS system, or in general to provide a modular interconnect system having the combination of compactness, reliability, and ease-of-maintenance of the present invention.
Instead, despite the sophistication and rapid development of components requiring optical interconnects, the experience of the telecommunications industry, and even the previous incorporation of optical connectors in LRM interconnect systems represented by the system described in U.S. Pat. No. 4,808,115, initial attempts at meeting specifications for optical interconnect systems have approached the problem as one of simply retrofitting optical connectors onto conventional electrical backplanes. For example, one proposed design involves mounting of individual optical connectors in a common frame to form a modular optical backplane, the optical backplane in turn being mounted behind an essentially conventional electrical backplane so that it can be separately removed for repair and maintenance.
While this arrangement facilitates the inclusion of optical connectors in the backplane, it has a number of disadvantages. For example, in order to service the electrical backplane, the optical backplane must be removed even if the optical backplane does not need servicing. In addition, this design does not provide an input/output connector for simplifying external fiber optic connections to the backplane, as opposed to interconnections between modules, forcing each separate connector on the module to be disconnected in order to remove the module, and because the previously proposed optical backplane design is simply piggybacked onto a standard electrical backpanel arrangement, the fiber optic interconnects must be routed around the central electrical connections using a T formation of the fiber ribbons in order to optimize in plane versus out of plane bends.
The present invention, in contrast, abandons any attempt to fit the optical backplane onto the standard electrical backplane, taking the unique approach of designing the electrical and optical elements of the backplane as separate modules, while still integrating the modules to form a common backplane which possesses the necessary dimensions, permits use of the backplane in an otherwise standard LRM rack, meets reliability standards critical for military and other avionics applications, and yet is more efficient to manufacture than previously proposed designs.